1. Field of the Invention
The present invention relates to a throw-away insert used in the milling of right-angle corners and the like and a milling cutter, e.g., an end mill or corner mill, that uses this insert.
2. Description of the Background Art
Japanese Utility Model Publication Number 2531557 and Japanese Laid-open Patent Publication Number Hei 11-333616 describes an example of a throw-away insert (also referred to below simply as insert) used with a negative/positive orientation to cut right-angle corners. Negative/positive orientation refers to mounting an insert so that a radial rake of the insert is negative and the axial rake is positive.
The insert described in Japanese Utility Model Publication Number 2531557 forms a roughly parallelogram shape and is a positive insert with a side surface intersecting at an acute angle with an upper surface serving as the rake face. The acute-angle corner side of the upper surface is used to cut the corner of the workpiece. The insert disclosed in Japanese Laid-Open Patent Publication Number Hei 11-333616 forms a roughly rectangular shape. A ridge line positioned at the intersection of a side surface and an upper surface serves as a main cutting section, and an end surface of a sloped surface axially projected from an end of a body serves as a secondary cutting section.
Throw-away inserts used for cutting are primarily sintered inserts. Sintered inserts are made by filling a mold with a raw material powder, shaping it with a press, and sintering the obtained shaped body. During sintering, changes in dimensions are unavoidable. Depending on the shape of the insert, powder density at different sections can vary during the shaping of the powder. The inserts obtained by sintering this type of shaped body have reduced dimensional accuracy after sintering, resulting in inferior cutting accuracy and attachment accuracy when attaching to a cutter body.
With positive inserts that use a parallelogram shape as the basic shape, such as the one described in Japanese Utility Model Publication Number 2531557, powder tends to fill up less at the acute-angle corners compared to the obtuse-angle corners. This leads to different amounts and densities for the powder that fills the acute-angle nose sections and the obtuse-angle nose sections, resulting in variations in the dimension changes taking place during sintering. This reduces the dimensional accuracy after sintering.
Also, the insert in the Japanese Laid-open Patent Publication Number Hei 11-333616 may be considered to have less powder density variation than the insert of the Japanese Utility Model Publication Number 2531557. However, since the ridge line axially projected from the end of the body is used as the secondary cutting section and since the sloped surface forming the secondary cutting section is used to axially support the insert, the small area of the sloped surface is further reduced when the secondary cutting section is damaged, leading to reduced axial support stability. Also, since the surface pressure of the support surface is increased by the reduction in the support surface, the tool life of the insert and the cutter body and the like may be reduced as well.
The object of the present invention is to overcome the problems of the inserts described in Japanese Utility Model Publication Number 2531557 and Japanese Laid-open Patent Publication Number Hei 11-333616 and to improve the dimensional accuracy of a sintered insert by reducing variations in powder density while using a structure that does not sacrifice support stability when there is damage to a secondary cutting section.